Electrophotography machines comprise an LED print head which is disposed to generate a pattern of light on a uniformly charged photo-sensitive drum. Specifically, light-emitting-diodes (LED) of the LED print head are selectively driven in dependence upon print data received by the LED print head. The regions of the photo-sensitive drum which are exposed to the pattern of light from the driven LED's become electrostatically charged thereby forming an electrostatic image on the surface of the photo-sensitive drum. These charged regions of the photo-sensitive drum attract and hold toner which is subsequently transferred from the drum onto paper. The toner is then fused to the paper by the application of heat.
LED print heads driven by conventional techniques have been deficient because they were incapable of printing multiple gray levels. That is, conventionally driven LED print heads can only print a single shade, black. Consequently, images printed by conventionally driven LED print heads comprise black regions where toner has been applied and white regions were no toner has been applied; the images do not contain intermediate shades of gray. Therefore, although conventional electrophotography machines can successfully reproduce text which includes only two tones, they have been ineffective at printing, for instance, pictures which must be printed with a variety of gray levels for accurate and effective reproduction.